Technical Reference — MEL calculator

Category

Date of discovery (start)

The day the defect was found and deferred. It is day 0 — not counted.

One extension — the same length again, once. Only if the MEL preamble allows it and it is approved before the interval runs out.

How it is counted

B · 3 calendar days: excluding the day of discovery.
C · 10 calendar days: excluding the day of discovery.
D · 120 calendar days: excluding the day of discovery.
A · the interval written in the item: calendar or flight days exclude the day of discovery; hours, cycles and flights count from the moment the item is deferred.
Last day: the interval ends at 23:59 of the last day, on the clock your MEL uses (usually UTC). Example: C found 01 MAR → days 1–10 are 02–11 MAR → runs out 11 MAR 23:59.
Extension: B, C and D only, when the MEL preamble says so: one extension, no longer than the original interval, approved before it expires.

REFERENCE ONLY. The MEL your organisation holds, its preamble and your procedures decide the interval. Check the item itself — some items carry their own limit.

MEL CALCULATOR